The present application generally relates to a locomotive diesel engine and, more specifically, to a system and method for controlling an exhaust aftertreatment system for a locomotive diesel engine. The present exhaust aftertreatment systems may be implemented with a locomotive two-stroke uniflow scavenged diesel engine.
FIG. 1a illustrates a locomotive 103 including a conventional uniflow two-stroke diesel engine system 101. As shown in FIGS. 1b and 1c, the locomotive diesel engine system 101 of FIG. 1a includes a conventional air system. Referring concurrently to both FIGS. 1b and 1c, the locomotive diesel engine system 101 generally comprises a turbocharger 100 having a compressor 102 and a turbine 104, which provides compressed air to an engine 106 having an airbox 108, power assemblies 110, an exhaust manifold 112, and a crankcase 114. In a typical locomotive diesel engine system 101, the turbocharger 100 increases the power density of the engine 106 by compressing and increasing the amount of air transferred to the engine 106.
More specifically, the turbocharger 100 draws air from the atmosphere 116, which is filtered using a conventional air filter 118. The filtered air is compressed by a compressor 102. The compressor 102 is powered by a turbine 104, as will be discussed in further detail below. A larger portion of the compressed air (or charge air) is transferred to an aftercooler 120 (or otherwise referred to as a heat exchanger, charge air cooler, or intercooler) where the charge air is cooled to a select temperature. Another smaller portion of the compressed air is transferred to a crankcase ventilation oil separator 122, which evacuates the crankcase 114 in the engine; entrains crankcase gas; and filters entrained crankcase oil before releasing the mixture of crankcase gas and compressed air into the atmosphere 116.
The cooled charge air from the aftercooler 120 enters the engine 106 via an airbox 108. The decrease in charge air intake temperature provides a denser intake charge to the engine, which reduces NOX emissions while improving fuel economy. The airbox 108 is a single enclosure, which distributes the cooled air to a plurality of cylinders. The combustion cycle of a diesel engine includes, what is referred to as, scavenging and mixing processes. During the scavenging and mixing processes, a positive pressure gradient is maintained from the intake port of the airbox 108 to the exhaust manifold 112 such that the cooled charge air from the airbox 108 charges the cylinders and scavenges most of the combusted gas from the previous combustion cycle.
More specifically, during the scavenging process in the power assembly 110, the cooled charge air enters one end of a cylinder controlled by an associated piston and intake ports. The cooled charge air mixes with a small amount of combusted gas remaining from the previous cycle. At the same time, the larger amount of combusted gas exits the other end of the cylinder via four exhaust valves and enters the exhaust manifold 112 as exhaust gas. The control of these scavenging and mixing processes is instrumental in emissions reduction as well as in achieving desired levels of fuel economy.
Exhaust gases from the combustion cycle exit the engine 106 via an exhaust manifold 112. The exhaust gas flow from the engine 106 is used to power the turbine 104 of the turbocharger 100, and thereby power the compressor 102 of the turbocharger 100. After powering the turbine 104, the exhaust gases are released into the atmosphere 116 via an exhaust stack 124 or silencer.
The exhaust gases released into the atmosphere by a locomotive diesel engine include particulates, nitrogen oxides (NOX) and other pollutants. Legislation has been passed to reduce the amount of pollutants that may be released into the atmosphere. Traditional systems have been implemented which reduce these pollutants, but at the expense of fuel efficiency. Accordingly, it is an object of the present disclosure to provide an exhaust aftertreatment system, which reduces the amount of pollutants (e.g., particulates, nitrogen oxides (NOX) and other pollutants) released by the diesel engine while achieving desired fuel efficiency.
The various embodiments of the present aftertreatment system are able to exceed, what is referred in the industry as, the Environmental Protection Agency's (EPA) Tier II (40 CFR 92), Tier III (40 CFR 1033), and Tier IV (40 CFR 1033) emission requirements, as well as the European Commission (EURO) Tier IIIb emission requirements. These various emission requirements are cited by reference herein and made a part of this patent application.